Question

how can I find potential molecular formula from molecular ion given m/z (mass/charge)?

ex: given m/z 148... solutions manual says potential molecular formula could be C10H12O

Answer 1

mass to charge ratio of protein is given by

m /z = (M + z H)/z (1)

m is the mass of the ion , z is no of protons, M is molcular mass

Eq.1 can be re-arrganged to give

M = z (m /z - H) (1)

m/z values of two adjacent peaks in the multiple-charge ion mass spectrum as m₁/z₁ and m₂/z₂ where z₁ = z₂ + 1. can be identified

  z ₂ = ((m₁/z ₁ )– H) / (( m₂/z ₂ )– (m₁/z ₁ )) (2)

determine the number of charges on any ion in the mass spectrum by knowing the m/z value of that ion and the m/z value of the immediately adjacent ion of lower m/z .The molecular mass M can be calculated from eq.1.